Reservoirs, Irrigation Demand, Drought, and Threatened Adfluvial Bull Trout in the Yakima River Basin, Washington

Storage reservoirs often serve dual purposes: water for anthropogenic use and habitat for sensitive species.  Understanding the effects of seasonal fluctuations in reservoir surface elevation and corresponding shifts in the thermal environment on food web structure and responses by species of concern can help us develop informed water management regimes that attempt to avoid adverse impacts, or evaluate the potential impacts of proposed changes in water management on key species. There is concern about meeting current and future irrigation demand in the Yakima River Basin, Washington, given an uncertain climate future. An integrated water management plan was designed to balance irrigation, recreation, and conservation needs in the basin. This plan proposes alterations to the structure and operation of Kachess and Keechelus Reservoirs to improve efficiency in water storage and use. Both reservoirs contain threatened populations of adfluvial bull trout. Here, we (1) evaluate the contemporary food web structure of Kachess and Keechelus Reservoirs, and (2) quantify key food web interactions as they relate to bull trout to provide a baseline for considering the potential impacts of altered water management. The first steps toward outlining operational targets that enhance water yield for irrigators while minimizing adverse impacts on bull trout.